With flourishing developments of multimedia technologies, many personal computers or servers are equipped with more hardware equipment (such as hard disk drive, card reader, compact disc burner and the like) to improve performance. Due to the power supply for the original hardware configuration has a fixed power capacity, when the added hardware equipment exceed the original power supply limitation, users have to procure a power supply of a greater capacity to meet the operation requirement. For the power supply vendors, trying to meet the requirement of a greater power supply capacity through a single power supply involves complicated techniques. It results in higher manufacturing cost. The size and heat dissipation problems also are difficult to overcome. Moreover, in the event that all of the hardware equipment is not being fully utilized during computer operation, electric power resource is wasted.
In view of these concerns, some vendors have adopted an approach that couples a plurality of power supplies in a parallel fashion. And a plurality of electric output connectors are provided to complement the higher and the lower power at the same time. FIG. 1 illustrates a technique disclosed in R.O.C. patent publication No. 00566760, entitled “Improved high capacity power supply”. It provides a high capacity power supply by coupling power supplies in a parallel fashion. It has output of +5V −5V and +3.3V. Another power supply has output of +12V and −12V. The individual power supply is controlled by a driving circuit. Then the power supplies are configured on a same base board in a parallel fashion through a pulse wave control circuit and a protection circuit. Such a structure has drawbacks, notably:
1. The internal circuit of each power supply has to be modified significantly. The power supply of different vendors has compatibility problem. This incompatibility problem even occurs to the power supply of different models purchased at different time. Hence once a power supply breaks down, the entire set of the parallel power supply has to be replaced. It is not economical.
2. In the event that two sets of power supply coupled in parallel fashion still cannot meet the hardware requirement, due to circuit design, it is not possible to add another power supply in the parallel fashion. Hence the expandability is limited. Even if the internal circuit of the individual power supply has been redesigned, the incurred cost is great. Moreover, for each additional power supply, one more control IC has to be added. The resulting cost increase is significant.
3. The power supply has to be coupled in parallel under the same power specification. It limits the coupled power capacity. To couple with a lower capacity power supply in parallel will result in not meeting the requirement of high power capacity. But to couple with a higher capacity power supply in parallel, the hardware equipment will result in waste of electric power resource when in use.